A high pressure tank equipped with a mouthpiece made of a metal, an inner shell (hereinafter called “liner”) made of a resin and an outer shell (hereinafter called “reinforcement layer”) made of a fiber-reinforced resin has been known as a tank filled with a high pressure fluid such as hydrogen gas. The mouthpiece is a member serving as an opening to fill the fluid into the high pressure tank or release the fluid contained in the high pressure tank and is provided on an open end of the high pressure tank.
A known technique employed to manufacture the high pressure tank is filament winding method (hereinafter referred to as “FW method”). The FW method winds reinforced fibers impregnated with a thermosetting resin such as an epoxy resin on the outer surface of a tank main body that is the liner equipped with the mouthpiece and then thermally cures the thermosetting resin included in the reinforced fibers, so as to form the reinforcement layer.
The FW method generally winds the reinforced fibers on the tank main body, while the tank main body held in a rotatable manner is rotated in the circumferential direction of the tank main body. The tank main body is rotated with the mouthpiece of the tank main body fixed to an FW device. In this process, the mouthpiece may rotate idly to prevent the reinforced fibers impregnated with the thermosetting resin from being adequately wound on the outer surface of the tank main body.
One proposed technique forms a mouthpiece in a serrate shape to suppress idle rotation of the mouthpiece (see, for example, Japanese Patent Publication No. 2013-167298A).
The internal pressure of the high pressure tank is varied in use. The liner made of the resin and the mouthpiece made of the metal have different expansion coefficients. Accordingly, a variation in internal pressure of the tank is likely to apply a stress to the reinforcement layer on the boundary between the mouthpiece and the liner and cause distortion in the reinforcement layer, due to the difference in expansion coefficient between the mouthpiece and the liner. In the technique disclosed in JP 2013-167298A, the mouthpiece is formed in the serrate shape and has a longer boundary between the mouthpiece and the liner compared with a mouthpiece formed in a circular shape. In this configuration, a variation in internal pressure of the high pressure tank is likely to cause distortion at a number of different positions in the reinforcement layer. Forming the mouthing in a simple circular shape is, however, likely to cause idle rotation of the mouthpiece as mentioned above.